This invention is generally in the area of delivery of agents for prevention of surgical adhesions, and specifically involves use of locally formed topical gel systems for controlled delivery of fibrinolysis enhancement agents, especially urokinase, for improved prevention of adhesions.
Adhesions in Surgery
The formation of adhesions, or scar tissue bridges, following surgery, remains a serious complication of many surgical procedures. These include pelvic, abdominal, spinal, tendon, ophthalmic, urinary, thoracic and other procedures. Adhesion formation is believed to occur through a series of events, one of which is the formation of fibrin bridges from a serosanguinous exudate occurring after surgery. The organs are first connected by thin fibrin bridges. Over time, these bridges become populated by cells, which may secrete collagen and otherwise stabilize the bridge. It has been observed that the level of cellular secretion of plasminogen activators, which normally cause the breakdown of fibrin by activating the enzyme plasminogen, can be decreased following injury to tissues. Thus, prevention of the stabilization of such fibrin bridges, and in particular enhancement of natural processes which can remove such bridges before their stabilization into adhesions, is highly desirable in the prevention of adhesions.
Cellular secretion of plasminogen activators, e.g., by the mesothelial cells that line the peritoneum, has been demonstrated by Vipond, et al., "Peritoneal Fibrinolytic Activity and Intra-abdominal Adhesions." The Lancet, 335:1120-1122 (1990), to be reduced following injury, leading to the lack of resorption of the fibrin bridges prior to maturation into a scar. In the peritoneal cavity, the particular fibrinolytic reduced in secretion was demonstrated to be tPA and not uPA.
Barrier Methods in Adhesion Prevention:
Several physical barrier methods have been utilized in the prevention of postoperative adhesions. These include sheets of oxidized regenerated cellulose (U.S. Pat. No. 5,007,916 to Linsky and Cunningham; U.S. Pat. No. 5,134,229 to Saferstein, et al.) sheets of expanded polytetrafluoroethylene (Boyers, et al., "Reduction of Postoperative Pelvic Adhesions in the Rabbit with Gore-Tex.TM. Surgical Membrane." Fertility and Sterility, 49:1066-1070 (1988)), thermoreversible hydrogels (U.S. Pat. No. 5,126,141 to Henry), and photopolymerized, resorbable hydrogels (U.S. Ser. No. 08/022,687 entitled "Photopolymerizable Biodegradable Hydrogels as Tissue Contacting Materials and Controlled-Release Carriers" filed Mar. 1, 1993 by Hubbell, et al., to which this application claims priority, the teachings of which are incorporated by reference herein). With the exception of the method of Hubbell, et al., these methods have ranged in usefulness, but in no case do the methods eliminate the formation of postoperative adhesions.
Use of Fibrinolytic enzymes in Prevention of Adhesions.
Various fibrinolysis enhancing agents have been used in attempts to prevent adhesions. Because of their availability and biological suitability, streptokinase (SK), urokinase (UK; also known as urokinase plasminogen activator, uPA), tissue plasminogen activator (tPA), and a modified recombinant tPA (Fb-Fb-CF) have been most widely tested. These agents all work by activation of the enzyme plasminogen, causing it to lyse fibrin. Other substances investigated for removal or prevention of fibrin strands have included proteolytic enzymes, drugs, and clotting inhibitors such as heparin, which tend to prevent deposition of additional fibrin, referred to herein as "fibrinolysis enhancing agents".
Fibrinolytic enzymes have been used in the prevention of postoperative adhesions, as reviewed by Dunn, "Tissue-type Plasminogen Activator and Adhesion Prevention." Prog. Clin. Biol. Res. 38:213-220 (1993), and "Adhesion, Adhesiolysis and Plasminogen Activators." Assisted Human Reproductive Technology, 13:130-137 (1991).
Tissue Plasminogen Activator (tPA).
Tissue Plasminogen Activator (tPA) has been shown to be of use in the prevention of postoperative adhesions, when delivered by minipump infusion, intraperitoneal injection, and topically. Sheffield describes the topical administration of tPA preferably by injection, but possibly in a phospholipid carrier, a salve or ointment, a polysaccharide composition, a thermoplastic polymeric gel or a hydrogel such as a polyoxyethylene-polyoxypropylene block copolymer, which releases over a period of between three hours up to seven days. Wiseman, et al. (J. Surg. Res. 53:362-368, 1991), describes the addition of tPA, a tPA analog, Fb-Fb-CF, and SK, alone or in combination with an absorbable sheet of oxidized regenerated cellulose, Interceed TC7 absorbable adhesion barrier from Ethicon, Inc., Somerville, N.J.
Streptokinase (SK).
Streptokinase (SK), the earliest plasminogen activator to become widely available, has been shown by some investigators to be effective in preventing adhesions and ineffective by others. SK has been shown to be effective in the prevention of postoperative adhesions when delivered by peritoneal injection (Meier, et al. "First Clinical Results of Intraoperative Application of Streptokinase-Streptokinase in Children." Langenbecks Archiv. fur Chirurgie, 366:191-193 (1985), Treutner, et al. "Postoperative, intraabdominelle Adhasionen-Ein neues standardisiertes und objektivierties Tiermodell und Testung von Substanzen zur Adhasionsprophylaxe.*" Lagenbecks Archiv. fur Chirurgie, 374:99-104 (1989)) and ineffective in other studies when similarly delivered (Verreet, et al. "Preventing Recurrent Postoperative Adhesions: An Experimental Study in Rats." Eur. Surg. Res., 21:267-273 (1989)). When delivered as a continuous infusion, it was not effective (Sheffield). When delivered from a degradable polymer matrix, it was somewhat effective (Wiseman, et al.).
Reports on side-effects of tPA differ widely, from none, at effective doses (Menzies and Ellis (Surgery. Gynecol. & Obstet. 172:362-366, 1991), or Sheffield), to severe at effective doses (Wiseman, et al.).
Fb-Fb-CF.
Fb-Fb-CF is a tPA analog (Phillips, et al., "The Effects of a New Tissue Plasminogen Activator Analogue, Fb-Fb-CF, on Cerebral Reperfusion in a Rabbit Embolic Stroke Model." Annals of Neurology, 25:281-285 (1989)) and was effective in the prevention of postoperative adhesions when released from a degradable polymer matrix (Wiseman, et al.) (J. Surg. Res. 53:362-368, 1992).
Genetic engineering is being applied to generate additional forms of plasminogen activators, plasmin, plasminogen, and other fibrinolytic agents, for example, as described in U.S. Pat. Nos. 5,223,408, 5,185,259, and 5,094,953.
Urokinase Plasminogen Activator (uPA).
The majority of studies with Urokinase Plasminogen Activator (uPA) have not demonstrated usefulness in preventing surgical adhesions. uPA has been investigated in the prevention of adhesions, as reported by Dunn (Chapter 13, p. 130-137, in Assisted Human Reproductive Technology, ed. E S E Hafez (Hemisphere Pub., New York, 1991) (1991). An initial study with uPA in several species was not successful. However, a second study by Gervin, et al., "A Cause of Postoperative Adhesions" Am. J. Surg. 125:80-88 (1973), did show efficacy. Dogs were treated with an intraperitoneal injection of large amounts of urokinase at the time of surgery. At dosages of 20,000 U/kg, there was allegedly a significant decrease in the formation of ileal adhesions.
However, no subsequent studies have demonstrated efficacy. For example, as reported by Rivkind, et al. "Urokinase Does Not Prevent Abdominal Adhesion Formation in Rats." Eur. Surg. Res., 17:254- 258 (1985), who studied the administration of urokinase in dosages between 5,000 and 100,000 U/kg administered intravenously, intraperitoneally, and intragastrically immediately postoperatively and at 48-72 hours post surgery. Moreover, uPA released continuously with minipumps at the site of injury did not reduce adhesions, as reported by Sheffield, et al. Another study in rabbits claimed to show efficacy with abrasion injury to the uterine horns, following administration of 10,000 U/kg urokinase either intraperitoneally or intravenously at the time of surgery and at 24 and 48 hours after surgery, both when blood was added to the peritoneal cavity and without added blood (injury in both cases), Birkenfeld and Schenker "The Effect of Urokinase in the Prevention of Intraperitoneal Adhesions; Role of Blood in Their Formation." Annales Chirurgiae et Gynaecologiae, 72:246-249 (1983). Notwithstanding the assertion of efficacy, reference to Table 2 of Birkenfeld and Schenker, shows that comparison between the group "Serosal abrading of the right uterine horn --No treatment" and the group "Serosal abrading of the right uterine horn--Urokinase treatment" demonstrates a difference with a p value of only approximately 0.2. By contrast, the group "Serosal abrading+application of blood on right uterine horn--No treatment" differs from the group "Serosal abrading+application of blood on right uterine horn--Urokinase treatment" with a p value&lt;0.02, both by Chi-squared test. Thus, the treatment with urokinase was effective only with the addition of an unnatural amount of blood.
In summary, uPA has been shown to be effective in the prevention of adhesions in only one study, and it has not been possible to reproduce this observation using normal conditions and normal standards for statistical difference. Efficacy with other fibrinolytic agents has also been mixed, with the best results for tPA being obtained only with repeated or continuous infusion of high dosages, and essentially no efficacy being observed with streptokinase.
The literature in this field is highly equivocal about the utility of any of these agents as reliable, clinically effective means for prevention of surgical adhesions.
It is therefore an object of the present invention to provide a reliable means for locally preventing surgical adhesions using fibrinolytic agents.
It is a further object of the present invention to provide a means for preventing surgical adhesions which is minimally invasive, biodegradable over the same period of time as healing occurs, and simply to use.
It is still another object of the present invention to provide a means for preventing surgical adhesions which uses low dosages of fibrinolytic agents.